Electrical drives with transmission system stages are often designed with an electrical machine, such as a synchronous machine, an asynchronous machine, a reluctance machine and similar, which is excited either by permanent magnets or electrically, and to whose output shaft a single or multi-stage transmission system is mechanically connected.
For example, in DE 4 334 590 A1 an electric motor with a hollow shaft is disclosed, which is connected to a differential transmission system having a spur gear, one output shaft of which is led through the hollow shaft of the electric motor. However, a spur gear transmission system has the disadvantage that in each case only one pair of tooth flanks transmits the forces and the torque to the following shaft. A planetary gear with a plurality of planet gears would enable a distribution of the forces over a plurality of tooth flank pairs, but for a uniform distribution of the forces over the individual planet gears precision is required in its mechanical production, with the result that such a solution is expensive. In addition, the planet gears in planetary gears typically have two contact points on the tooth flanks at which transmission system losses are generated as a result of sliding movements.
From WO 2004/047256 A1 a generator with multiple outputs is of known art, wherein two generator units are mounted inside the housing around a main shaft.
Furthermore, DE 10 2013 213 847 A1 and the corresponding WO 2015/007441 A2 disclose arrangements of a plurality of electrical machines that are connected to a downstream transmission system. Here it is proposed to assign a plurality of pole pairs, e.g. four, to single pole rotors. The rotors are arranged radially offset relative to each other. A disadvantage here is that the disclosed downstream transmission system cannot implement opposite directions of rotation of adjacent rotors at the same rotational speed. A further disadvantage is that each rotor requires a full stator design, because no geometric simplifications can be introduced into the stator build to reduce the material required. In particular, the disclosed topologies cannot represent advantageously material-reduced three-phase alternating current topologies, such as four two-pole or four-pole rotors in a three-phase stator arrangement with a corresponding transmission functionality.
From EP 0721248 A2 an electrical drive device with a plurality of rotors excited by permanent magnets is of known art, with three stator poles assigned to each rotor. This drive device is intended for dry shavers, wherein the rotors rotate without any mutual mechanical connection, as is usual in shavers. This has the disadvantage that there is no preferred stage in the transmission system that increases the torque.
Another arrangement with a plurality of rotors and a common stator is shown in DE 10 2009 010 162 A1. Here the plurality of rotors is arranged in the form of a matrix, wherein all shafts rotate in the same direction, as a result of which a complicated stator geometry is required.
A similar solution is specified in U.S. Pat. No. 5,780,950 A, where a plurality of rotors similarly interacts with a common stator, wherein the stator coil ends are in each case directed towards another rotor. A disadvantage is that although all the rotors are mechanically connected to a stage of the transmission system, they rotate in the same direction and therefore have the characteristic of single-phase machines with fluctuating torques, which cause an uneven introduction of torque into the connecting transmission system. In particular, it is not possible to generate a three-phase alternating current arrangement that could feed in a uniform torque to each sub-rotor.
A further arrangement with a plurality of parallel rotors, and a magnetic circuit acting on a plurality of rotors, is specified in EP 0678966 A1. However, the geometry requires complex distributed coil systems, as a result of which a significantly complex stator build is required.
Finally, DE 2006 386 C1 also shows a multi-rotor arrangement that interacts with a rotating field of a common stator system. As a result of the matrix-like arrangement it is not possible to have an economical build of transmission system to connect the rotors, and by virtue of the target applications (centrifuges), this is also not the intention.
The object of the invention is to create an electrical machine system as described in the introduction, which, on the one hand, avoids the disadvantages cited above, and on the other hand, can work and be operated more economically by virtue of a new machine structure.
This object is achieved by the invention, which provides an electrical machine system in accordance with the accompanying claims.
The invention thus provides for a machine system with an arrangement of a plurality of sub electrical machines that are mechanically connected by way of a transmission system. Here a compact design of the machine system consisting of the sub electrical machines is made possible, as certain parts of the sub-machine can be omitted by virtue of the geometric arrangement, because the magnetic flux components of adjacent sub-machines compensate for each other element-by-element and thus magnetically active material can be saved, that is to say, eliminated. On the other hand, the mechanical coupling of the sub-machines can advantageously be embodied as a mechanical planetary gear (or mechanical planetary gear train or mechanical epicyclic gear train) with a desired transmission ratio, as a result of which components of the planetary gear, such as bearings, couplings and housing parts, can be saved, that is to say, utilised twice, compared to a discrete build of electrical machine and functionally separate planetary gear. Moreover, the planet gears connected to the sub-machines of the present machine system have only one contact on the tooth flank, as a result of which the losses can be significantly reduced compared to a normal planetary transmission system.
A further advantage is that the sub electrical machines transfer the sub-torques or sub-forces that they develop to a planet gear assigned to the sub-motor by a direct mechanical connection, irrespective of the mechanical manufacturing tolerances. Accordingly, there is no need to split a single shaft torque of the electrical machine by way of a gear onto planetary gears; rather the torque is split directly by means of the sub-machines. Thus, the power of each sub-machine can be apportioned into 1/nth of the power of a single assigned electrical machine (where n=number of planet gears or sub-machines). In addition to the greatly simplified design, another noteworthy advantage ensues: since experience has shown that the peripheral speed of high rotational speed drives is predominantly limited to a few 100 m/s for strength reasons, significantly more electrical power can be installed in the same volume with the same limited peripheral speed of the sub-rotors. If, for example, a rotor is split into four sub-rotors with the same total rotor surface area, the sub-rotors then have half the diameter of the original rotor. Assuming the same specific thrust per unit surface area in the air gap, half the diameter, or half the periphery, of the original rotor signifies half the thrust per sub-rotor. Multiplying this by half the radius of the original rotor, each sub-rotor thus delivers a quarter of the original torque. In total, the splitting into surface area-neutral sub-rotors delivers the same torque, that is to say, the same power is generated with the same rotational speed of the sub-rotors as was originally possible. The same power output can therefore be achieved with the present system with half the peripheral speed, and a great advantage is thereby obtained in the mechanical implementation. Thus in principle, there is still a reserve enabling the rotational speed and thus the installed power output to be doubled with a restoration of the original peripheral speed. It is also advantageous that the transmission functionality that effects the mechanical coupling can be utilised as a transmission ratio from rotor speed to transmission system output drive speed.
Furthermore, it is beneficial that the coils of the multi-machine system can be connected to form a multi-phase alternating current winding system with any number of phases (or branches), preferably a three-phase alternating current winding system.
In a preferred embodiment, the sub-machines can be synchronous rotors with permanent magnet excitation, electrical excitation and/or reluctance characteristics. On the other hand, the sub-machines can also be asynchronous rotors in the form of a squirrel cage rotor and/or a slip ring rotor.
The activation of the coil system can advantageously be carried out by way of power electronic actuators in accordance with known activation methods for three-phase alternating current machines; furthermore, it is possible to determine an average electrical rotor position of the sub-machines by means of sensor-less methods, based on mathematical models, and a calculating unit. AT 508 854 B should be mentioned as an example. Mathematical models are also specified in Schrödl, M. “Sensorless Control of A.C. machines”, VDI Progress Report, Series 21, No. 117 (VDI-Verlag Düsseldorf 1992).
The mechanical coupling of the sub-machines can also be such that the execution of a resulting linear movement is achieved in a manner known per se.
For ease of adjustment, it is also advantageous if the average angular positions of the sub-machines rotating in different directions can be altered mechanically relative to each other during operation.
The machine system can have a shaft that carries one or a plurality of transmission system elements, wherein the transmission system element(s) mechanically couple(s) the sub-machines, wherein the shaft is mechanically connected to a differential transmission system; here the shaft is preferably embodied as a hollow shaft to save space.
In what follows, a two-branch (or phase) and a three-branch (or phase) structure, in each case based on four sub-machines 1, 2, 3, 4, will be converted into an advantageously constructed two-branch or three-branch planetary motor.